Field
This disclosure is generally related to power allocation in the downlink of a multi-user multiple-input multiple-output (MU-MIMO) system. More specifically, this disclosure is related to a method and system for allocating downlink transmission power based on a scheduler utility metric while satisfying power restriction conditions.
Related Art
Multiple-input multiple-output (MIMO) systems have tremendous potential in increasing the average throughput in cellular wireless communication systems. The performance gain in channel capacity, reliability, and spectral efficiency in single user (point-to-point) MIMO (SU-MIMO) systems has spurred the inclusion of SU-MIMO in various cellular and wireless communication standards. In cellular networks where spectrum scarcity/cost is a major concern, the ability to reuse spectrum resources is critically important. To further increase spectral efficiency in cellular networks, the spatial diversity of the users can be exploited to allow multi-user MIMO (MU-MIMO) transmissions.
In a wireless MU-MIMO system, a base station (such as an eNode-B in an LTE network) equipped with multiple antennas is capable of serving multiple user equipments (UEs), each of which may be equipped with one or multiple antennas, on the same time-frequency resources. On the downlink (from the eNode-B to the UEs), the eNode-B sends different data streams to the different UEs. Note that the broadcasting nature of the downlink means that signals intended for one UE may cause interference at the other co-served UEs. To maximize the overall system throughput, various precoding techniques can be used, in which the same signal is emitted from each of the transmit antennas with independent and appropriate weighting. For example, zero-forcing precoding allows the multiple-antenna transmitter to nullify multi-user interference signals.
In addition to precoding, power allocation to the co-served UEs also impacts the system performance. However, conventional MU-MIMO transmission schemes often rely on naïve power allocation schemes, where the system allocates equal transmission or receiving power to each UE.